Rule:  

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Sid: 1882

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Summary: 
This event is generated by the use of a UNIX "id" command. This may be indicative of post-compromise behavior where the attacker is checking for super user privileges gained by a sucessful exploit against a vulnerable system.

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Impact: 
Serious. An attacker may have gained user access to the system.

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Detailed Information:
This event is generated when a UNIX "id" command is used to confirm the user name of the currenly logged in user over an unencrypted connection. 
This connection can either be a legitimate telnet connection or the result of spawning a remote shell as a consequence of a successful network exploit. 

The string "uid=" is an output of an "id" command indicating that a check is being made on the users current id.

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Attack Scenarios: 
A buffer overflow exploit against an FTP server results in "/bin/sh" being executed. An automated script performing an attack, checks for the success of the exploit via an "id" command.

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Ease of Attack: 
Simple. This may be post-attack behavior and can be indicative of the successful exploitation of a vulnerable system.

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False Positives: 
This rule will generate an event if a legitimate system administrator executes the "id" command over an unencrypted connection to verify the privilege level available to him.

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False Negatives:
None Known

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Corrective Action: 
Ensure that this event was not generated by a legitimate session then investigate the server for signs of compromise

Look for other events generated by the same IP addresses.

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Contributors: 
Sourcefire Research Team
Brian Caswell <bmc@sourcefire.com>
Nigel Houghton <nigel.houghton@sourcefire.com>
Snort documentation contributed by Anton Chuvakin <http://www.chuvakin.org>

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Additional References:
